Mountain Biking - loud cranking sound

Hi all,
I've had my bike for about two months and am having so much fun w it. However, it occationally makes some loud noise and it makes me think the chain slips. It happens when I depart AND when I apply (heavy) pressure on the pedal. It doesn't make this noise every time though. Anyone has any idea? By the way, the bike is a Trek 4500. Thanks for your input.
Luke

If you continually start in a really hard gear you are really mashing several parts on your bike. Try to do a start in an easier gear. It could be slipping because

a) Chain is stretched
b) Cassette is worn in the gear you use most
c) The freewheel is 'too' whobbly and when you really mash down it turns in just enough to force a skip

All 3 are feasible and without being there to watch and listen myself I can't offer much more.

It could also be a loose crank. I used to get a loud cracking noice. It was where the crank arm engages with the spline. I have also had a loose bottom bracket which gave a similar sound. :)

yea i am gonna hafta agree with the bottomw bracket. Loose bottomw bracket gave my bike a clicking noise evertime i pedal hard. Havn't fixed it yet but i will soon

Originally posted by mindbogger
yea i am gonna hafta agree with the bottomw bracket. Loose bottomw bracket gave my bike a clicking noise evertime i pedal hard. Havn't fixed it yet but i will soon

You can strip the thread in the bb tube (I forget the name) and screw it so bad you need a new frame...thats the type of thing I tighten right away :)

Originally posted by Maelstrom
You can strip the thread in the bb tube (I forget the name) and screw it so bad you need a new frame...thats the type of thing I tighten right away :)

ohhh shoot.....better start tightning....thanks for the heads up...was gonna go for an evening ride but better cancel it.

Thanks mael

It does take time to screw it up but I don't take chances. I messed up my commuter way back...I hate replacing frames...same with loose headsets...never ride with one of those either.

You just got it right? Heck, I'd take it back to the shop and ask for your "should be included with all new bike purchases" free 30 day tune-up!

Even if it's past the 30 day, any respectable shop should provide you with an "initial Break-in period adjustment".

L8R